Extensive formations of organic-bearing dolomitic marlstones exist throughout the western part of the United States, principally the mountain states of Colorado, Utah and Wyoming. This rock is ordinarily called "oil shale" since it contains considerable amounts of organic material termed "kerogen", which upon heating produces a hydrocarbon-type oil. The kerogen-bearing rocks occur in beds of varying oil content, with individual strata bearing as much as 75-95 gallons of shale oil per ton of rock ore.
According to the U.S. Bureau of Mines: "The term `oil shale` as commonly used, covers a wide variety of laminated, solidified mixtures of argillaceous sediments and organic matter having the common property of yielding oil upon destructive distillation, yet being but slightly susceptible to the action of solvents." Therefore, the term oil shale, as used herein, is not restricted to the organic-bearing dolomitic marlstones of the Green River formation.
Such kerogen-bearing rock (oil shale) is found in the Green River formation of the Piceance Creek Basin in Northwestern Colorado. This formation extends into the Uinta Basin of Utah and the Washakie Basin of Wyoming. Various oil shale-bearing members of the Green River Formation contain strata with continuous sequences which assay from 10 to 50 G.P.T. It is these members which are of principal initial interest to the recent bonus bidders for federal oil shale leases in Colorado and Utah.
The kerogen-bearing rock (oil shale) in the Green River Formation also contains sodium mineralization. These authigenic sodium-containing minerals include, principally, nahcolite, trona and dawsonite, with other significant sodium-containing minerals including shortite and halite. Nahcolite is a natural, crystalline, generally transparent to whitish, sodium bicarbonate mineral. In the Piceance Creek Basin the nahcolite occurs in two basic ways: disseminated (intermingled) in the oil shale, ranging from minute crystals to "rosettes" occurring in sizes of from about 1/4 inch to several feet in diameter, and in beds in the Saline Zone of the Parachute Creek member of the Green River Formation. The Saline Zone beds may range from 3-10' in thickness, and assay as high as 95% NaHCO.sub.3, with 30-90% being typical, the balance being oil shale rock and associated minerals. The Saline Zone itself ranges from 600-900' thick in the Piceance Creek Basin and is estimated to contain recoverable reserves of 12,000 tons/acre bedded nahcolite, 194,000 tons/acre disseminated nahcolite, 37,000 tons/acre dawsonite, and 306,000 Bbl shale oil/acre. Nahcolite is useful as an SO.sub.x air pollution control sorbent, and as a feedstock for production of soda ash.
Dawsonite, NaAlCO.sub.3 (OH).sub.2, occurs disseminated in oil shale, and is also present in the Saline Zone in assays up to 30%, with dawsonite-enriched zones typically running 8-14%. Dawsonite can be converted initially to sodium aluminate, an air and water pollution control agent, and eventually to alumina, which like bauxite is a feedstock for aluminum production.
Trona, Na.sub.2 CO.sub.3.sup.. NaHCO.sub.3.sup.. 2H.sub.2 O, is also present in beds, principally in Wyoming. Small amounts (1-5%) of trona, thermonatrite Na.sub.2 CO.sub.3.sup.. H.sub.2 O, and natron, Na.sub.2 CO.sub.3.sup.. 10H.sub.2 O may be present with nahcolite in the Piceance Creek Basin area of Northwestern Colorado. Trona is principally useful as a feedstock for production of soda ash.
In mining and processing nahcolite or trona for the sodium values, presence of oil shale is undesirable, lowering the run-of-mine sodium minerals assay, interfering with processing, and posing a disposal problem. Conversely, in the mining and processing of oil shale for the shale oil values, the presence of soluble sodium minerals is also undesirable. In extracting shale oil from the oil shale rock, retorting (heating) processes are employed. However, in some retorting processes, presence of minor quantities of sodium mineralization tends to combine with the silica, calcite, dolomite, feldspars, and gibbsite (Al(OH).sub.3) of the shale to form a glassy clinker that may plug the retort. In addition, the retorting converts dowsonite to sodium aluminate, and both nahcolite and trona to crude soda ash. All those materials in the retorted waste shale (processed oil shale rock) are water soluble. Disposal of the waste shale thus poses a serious water pollution problem since the soluble sodium values can leach from the shale, increasing ambient salinity. Since a mature oil shale industry would produce 13 billion tons of waste shale in about 30 years, even presence of only 1-5% of sodium minerals would contribute significantly to sodium alkalinity, if left unchecked.
One approach to these problems is multi-mineral development. This approach includes mining an oil shale of lower grade with respect to shale oil, but one that contains significant amounts of dawsonite and/or nahcolite. The minerals would be separated and each processed for their intrinsic values. In the Piceance Creek Basin the preferred mining would be underground in the Saline Zone of the Parachute Creek member, with all the waste disposed of by backfilling in the mine. A major problem to multi-mineral development is the lack of a relatively inexpensive, effective means of separating the nahcolite from the oil shale and dawsonite.
There exists, therefore, a need for a simple, relatively inexpensive, effective, controllable process for handling a wide variety of oil shale rock and sodium mineral-containing ores and separating the components from each other.